Null-modem is a serial communication method to connect two data terminal equipments (e.g., computers, terminals, printers, etc.) together directly using a special null-modem serial cable. The original RS-232 standard, which is a standard for serial binary data interconnection, only defines connections between data terminal equipments and data communication equipments (e.g., modems), but not between two data terminal equipments. As such, a typical, straight-through RS-232 cable cannot be used to connect two data terminal equipments. To facilitate communication between two data terminal equipments with serial interfaces, a transmit line and a receive line are cross-linked to establish a null-modem connection.
A null-modem cable is an RS-232 serial cable with the transmit line and receive line cross-linked. A regular, straight-through RS-232 serial cable also can be used together with a null-modem adapter. The null-modem adapter contains the necessary cross-links between the signals. When switching between a regular RS-232 connection and a null-modem connection, the null-modem cable must be manually swapped with a regular RS-232 cable. Similarly, if a null-modem adapter is used, the null-modem adapter must be manually removed when switching to a regular RS-232 connection.
When determining whether two data terminal equipments require a regular RS-232 connection or a null-modem connection, a user must manually swap between a regular RS-232 cable and a null-modem cable to test which cable works with the data terminal equipments. Such manual swaps are labor intensive and inconvenient. Furthermore, the two cables or null-modem adaptor required to switch between connections clutter the interconnections between the data terminal equipments with extra hardware.
In view of the foregoing, there is a need to provide a more convenient apparatus and method for enabling a null-modem connection with less clutter and hardware.